The field of the invention is headphones, including headphone-microphone headsets.
Headsets are commonly used by telephone operators, receptionists, and others who need to keep their hands free while listening and speaking over a telephone or other voice link. Typically these headsets will have a headband passing over the user's head, with an earphone at each end of the band and a microphone riding at the end of a boom extending from the headband. A lightweight cable, typically having three or four wires, leads from the headset to a telephone connection. The cable is attached to an earphone at one end of the headband to keep it out of the way. Often, the cable is coiled to provide a quasi-variable length interconnection.
The headset should be both tough to avoid damage, and light in weight so as not to tire the user, who often will wear the headset continuously through a work shift.
The headband is resilient and shaped into an arc so that it must be slightly sprung to fit over the head; the resulting friction force holds the band in place on the user's head. Since the band is the largest piece in the typical headset, its design is important in obtaining a durable, light headset.
Some headsets employ a single earphone, which saves some weight and expense. However, double earphones allow better hearing, both by doubling the sound energy to the user and by partially blocking outside noise from both ears. If double earphones are used, then electrical connection must be made to both earphones.
Since the cable is attached to the headset at one end of the headband near one of the earphones, two leads (conductive wires or lines) must be run along the headband to the other earphone. If no leads are run over the headband, then a separate cable must be run to either earphone. This is done in some belt-clip radios and tape decks, such as those sold by Sony Corporation under the trade name "Walkman." The two-cable arrangement is inconvenient when the cables are to be put over the shoulder, and the likelihood of cable damage is increased, both because there is an extra cable to be broken and because the two cables often become twisted.
To run the signal leads over the headband also causes design problems. The wires should be a fine gauge to keep the weight and cost low but they must resist breaking and tearing during both manufacture and use. They must be held closely to the headband or they will snag on something and break. They should be hidden for aesthetic reasons requiring extra manufacturing steps.
A better headset design would have fewer and sturdier parts than the band, wires, and wrapping structure. Ideally, the band would consist of the minimum number of parts: two conductors and one insulator. It should be sturdy enough to resist abuse and wear. If the signal conductors are fine wire leads, then they should be protected to avoid snagging and breakage.
Besides a tough, light headband, another requirement of a headset is that it be comfortable for long wear. A common source of discomfort in many headbands is pressure against the outer ear by the earphones.
A certain amount of force against the ears is required to hold the headset in place. As mentioned above, only friction is available to prevent the earphones from sliding sideways away from the ears. The sideways force to resist such sliding is a function of the coefficient of friction of the earphone against the ear, and the force pushing the earphone against the head. Given the mass of the earphones and headband and the friction coefficient, the minimum force is fixed.
Even with a light-weight headset and soft, high-friction cushion material such as foam, the force required is still great enough that the ears will become sore if the needed force is concentrated on one part of the ear. This will happen if the earphones are cocked, and do not sit squarely on the outer ear.
To prevent this, prior-art earphones have used various hinged joint structures to allow free rotation of the earphones.
One approach is to use ear plug-type earphones rather than larger external earphones. These, however, tend to clog with ear wax, may make the ear canal sore with long use, and cannot easily hold a microphone boom and its hinge.
With external earphones, prior designs have employed two basic approaches. The first is ball-and-socket; the second is external-yoke gimbals.
The ball-and-socket joint is simple to design and make with plastics, which allow a snap-in design. However, it has functional drawbacks.
First, the headband cannot stay close to the user's temple because the ball-and-socket joint is relatively thick. It will normally will be directly behind the sound transducer, so the whole earphone must be thicker still. The earphone must rotate about, and clearance is needed for the edge to swing without hitting the headband. All this means that the headband must be coupled to the earpiece a relatively far distance from the side of the head, which can lead to snagging.
Second, the earphone can rotate in all directions, including rotation about an axis pointing into the head (parallel to the ear canal). This means that when a microphone boom is attached to one of the earphones, the weight of the boom will rotate the earphone and the boom will droop. The telephone cable may also rotate out of its position on the bottom of the earphone and wrap about the ear.
The external-yoke gimbal design usually employs an outer yoke rotating on a pivot pin lying along the headband, and an inner ring whose hinge axis is horizontal. The two hinge axes are crossed, which allows earphone rotation in any direction.
The gimbal structure is complex and, being external to the headset structure, is prone to damage. It is also bulky: if the gimbal is small it must be outside the earphone, making for a thick structure as with the ball-and-socket joint; if the gimbal rings or yokes surround the earphone, the width is very great.
Both the ball-and-socket and the external-yoke designs place the center of rotation of the earphone near the geometrical middle of the earphone. The middle of the earphone, where the sound transducer is located, is in use placed directly over the ear canal for best hearing. The resilient force of the bowed headband is exerted at the center of rotation, and the force is evenly distributed around the perimeter of the earphone, that is, evenly distributed in a circle centered on the ear canal.
This distribution of force is not the ideal. The upper parts of the outer ear extend farther away from the sound-sensitive ear canal than do the lower parts: in fact, the only lower part to speak of is the earlobe. A moderately-sized earphone edge will push against the upper parts of the outer ear and skirt the lower parts. The upper parts are more sensitive, having delicate cartilage structures; pressure against them is more uncomfortable than pressure against the earlobe. The sensitivity is increased if eyeglass frames are trapped between the outer ear and the head.
A better distribution of pressure would exert greater force against the areas below the ear canal. These areas include the ear lobe, neck, and jaw. The prior art does not teach this distribution of force.